Various forms of pressure-sensitive adhesive sheets are used in the medical field, such as surgical tape, adhesive bandage, film dressing materials for wound treatment, a base material for fixing electrode for electrocardiographic measurement and the like. Many of the adhesives used for conventional medical pressure-sensitive adhesive sheets are made of acrylic polymers. Acrylic polymer is generally applied, for example, to a supportive substrate and release paper after adjusting viscosity with an organic solvent and the like. The organic solvent used for adjusting the viscosity is removed by volatilization after application. In so doing, the organic solvent is sometimes not removed sufficiently (insufficient drying), and the organic solvent may remain in the adhesive. When a pressure-sensitive adhesive sheet having a constitution where an adhesive directly touches the human body, such as an adhesive bandage and the like, is not dried sufficiently, the organic solvent remaining in the adhesive, which is absorbed into the body from the skin, may cause inflammation such as exanthema and the like. In addition, the organic solvent removed in the drying step is feared to cause environmental pollution and endanger the health and safety of the workers.
As a production method of conventional solvent-free pressure-sensitive adhesive tapes, a hotmelt method comprising heating, kneading and/or melting an adhesive for hotmelt and applying the same to a substrate, an emulsion method comprising applying an emulsion adhesive to a substrate and drying the same, an extrusion polymerization method comprising extruding a thermally polymerizable monomer liquid on a substrate while heating, kneading and polymerizing in a heating barrel, a photopolymerization method comprising applying a photopolymerizable monomer liquid to a substrate and exposing the same to light irradiation in an inert atmosphere to allow polymerization and the like are known. They are unsatisfactory from the viewpoints of workability (introduction into apparatus for light irradiation, reaction time), cost and the like, and from the viewpoints of adhesion performance such as adhesion to the skin, irritation, glue remainder and the like, and no production method can be preferably used for medical pressure-sensitive adhesive sheets such as adhesive bandage and the like.
As one embodiment of solvent-free adhesives, adhesives using urethane crosslinking, which use an oxyalkylene polymer, are known (JP-A-7-310066, JP-A-2002-60456). The aforementioned adhesives have been reported to be superior in adhesion to the skin, moisture permeability, water absorbability and the like. However, the adhesive is associated with problems in that the curing speed is difficult to control because of urethane crosslinking, and unreacted isocyanate has toxicity.